article: Which part of the world has the most nearsighted students? Just look around you-it's East Asia. _ school leavers in major East Asian cities are nearsighted, according to the BBC. Experts say books and video games are not to blame. East Asian students, they say, aren't getting enough sunlight.
  People become nearsighted because their eyeballs grow out of shape and light entering their eyes cannot focus correctly. The body can produce a chemical called dopamine   to stop eyeballs from changing shape. And guess what scientists have just discovered? Sunlight can help our bodies produce more dopamine, reported AFP.
  According to the study, primary school students in Singapore spend only 30 minutes outdoors every day; in Australia, by contrast, kids spend about three hours a day outside. As a result, fewer children in Australia are nearsighted-only 10 percent, compared with 90 percent in Singapore.
  "Children in East Asia basically go to school... go home and stay inside. They study and they watch television," Ian Morgan of the Australian National University told AFP.
  But being a bookworm or a couch potato does not directly harm the eyes, added Morgan. "As long as they get outside, it doesn't seem to matter how much study they do," he explained. "There are some kids who study hard and get outside and play hard and they are generally fine. The ones who are at major risk are the ones who study hard and don't get outside. As a result of massive   educational pressures and the construction   of a child's day, the amount of time they spend outside in bright light is minimized."
  Experts suggest children should stay outside for two to three hours every day. This can include time spent in the playground and walking to and from school.
question: What is the main reason for the large number of nearsighted students in East Asia, according to scientists?
options: Too much reading or gaming. Lack of sunlight. Genetic reasons. Lack of exercise.